1. Field of The Invention
The present invention relates to a secondary battery charging device that controls charging of a secondary battery and a secondary battery charging system that performs charging of the secondary battery.
2. Description of the Related Art
Mobile terminal devices, such as a personal digital assistant (PDA) and a mobile phone, can send and receive a large volume of information in a short time and they are used in many different fields.
Such a mobile terminal uses a secondary battery as its power source and it becomes necessary to charge the secondary battery when a charged amount falls below a pre-set value during use of the mobile terminal.
A charging device that charges the secondary battery by using natural energies, such as solar power generation and wind power generation, is widely known as a power generation source of electricity used for the above-mentioned charging (refer to JP-A-2004-166404, for example).
Further, in general, secondary batteries and electronic devices equipped with the secondary batteries have a protection timer, which is provided for the purpose of overcharge protection, and the protection timer performs a control in which charging is forcibly stopped when a pre-set charging time elapses.
Here, in some cases, a function of the protection timer is set off before the charged amount reaches a fully-charged amount, when an elapsed time of the protection timer exceeds the charging time.
Therefore, there is a charging method (refer to JP-A-7-123602, for example) that monitors a change in a charging current and re-sets the charging time of the protection timer when the charging time is prolonged due to decreased charging current.
Further, there is a charging method (refer to JP-A-6-38392, for example) that monitors a remaining capacity of the secondary battery and re-sets the charging time of the protection timer when the remaining capacity is less than the fully-charged charging amount.